pcu.py: Introduce PcuDummy class

It will be used in later commits by BTS without proper PCU control such
as NanoBts.

Change-Id: I37ba38f7d81134e5f0ca28fa684fdb09c753bb04

src/osmo_gsm_tester/pcu.py

@@ -46,4 +46,15 @@ class Pcu(log.Origin, metaclass=ABCMeta):
         """Start the PCU. Must be implemented by subclass."""
         pass
 
+#------------------------------------------------------------------------------
+
+class PcuDummy(Pcu):
+    """PCU for BTS without proper PCU control"""
+
+    def __init__(self, suite_run, bts, conf):
+        super().__init__(suite_run, bts, conf, 'PcuDummy')
+
+    def start(self):
+        pass
+
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